1. Field of the Invention
This invention relates to relighting digital images, and more particularly, to methods and apparatuses for using various types of diffusion processing for removing a first illumination from an image and reapplying a new illumination thereto.
2. Description of the Related Art
Images may contain variations in intensity which are introduced by the light source used to illuminate the subject and/or scene composing the image. These intensity variations may be undesirable as they can be visually distracting and reduce the aesthetic quality of an image. In order to improve the presentation of the image, it may be desirable to change the appearance of the illumination in the image. Changing the illumination is referred to herein as relighting.
The original unwanted illumination may manifest itself in the form of edge artifacts, which are referred to herein as spurious edges. Spurious edges can be distracting because they can mask real edges in the image, where real edges, which are the result of the underling structure of the subject or scene within the image, contain information typically of most interest to image users. Spurious edges, as well as other undesirable illumination variations, can be removed and changed through image relighting techniques.
One approach to remove the original illumination can be accomplished with illumination normalization techniques. Conventional illumination normalization techniques include level compression techniques to mitigate the appearance of illumination variations. Some level compression techniques use logarithmic functions to compress the dynamic range of the image, thus reducing the perception illumination gradients. Other techniques may use statistical approaches such as histogram stretching or equalization. Histogram approaches may seek to alter the intensity distribution of the image to improve overall contrast and reduce the effect of unwanted variations in intensity due to illumination. However, such conventional techniques may have difficulty compensating for sharp spurious edges, and may further cause other global variations in intensity which may be undesirable.
If the original illumination is not properly removed, then the application of a new illumination to relight the image may not appear natural, and thus be less desirable. Accordingly, there is a need for approaches to effectively remove an old illumination from the image so another illumination can be applied to perform image relighting.